diff --git a/vcsserver/remote/hg_remote.py b/vcsserver/remote/hg_remote.py
--- a/vcsserver/remote/hg_remote.py
+++ b/vcsserver/remote/hg_remote.py
@@ -23,6 +23,7 @@ import sys
 import urllib.request
 import urllib.parse
 import hashlib
+import traceback
 
 from hgext import largefiles, rebase
 
@@ -759,6 +760,24 @@ class HgRemote(RemoteBase):
         self._factory.repo(wire, create=create)
 
     @reraise_safe_exceptions
+    def assert_correct_path(self, wire):
+        cache_on, context_uid, repo_id = self._cache_on(wire)
+        region = self._region(wire)
+
+        @region.conditional_cache_on_arguments(condition=cache_on)
+        def _assert_correct_path(_context_uid, _repo_id):
+            try:
+                self._factory.repo(wire, create=False)
+            except Exception:
+                path = wire.get('path')
+                tb = traceback.format_exc()
+                log.debug("Invalid Mercurial path `%s`, tb: %s", path, tb)
+                return False
+            return True
+
+        return _assert_correct_path(context_uid, repo_id)
+
+    @reraise_safe_exceptions
     def lookup(self, wire, revision, both):
         cache_on, context_uid, repo_id = self._cache_on(wire)
         region = self._region(wire)